Copper oxide rectifier



Patented Dec. 8, 1942 UNITED STATES PATENT OFFICE- I I corPEa :nainorm l Carl C. Hein, Forest Hills, ol' to Westinghonse Electric Manufacturing Company,

East Pittsburgh, vania Pa., a annexation of Pennsyl- 9 Claims.

My invention relates to current rec-tifying apparatus and has particular relation to rectifiers of the coppor-copper-oxide type.

Because of certain inherent physical and chem.- ical properties, the eld of use of copper-copper', oxide rectiiiers constructed in accordance with the vteachings of the prior art is severely limited. A rectifier unit cannot be operated continuously to yield an output potential greater than 3 to 6 volts Moreover difficulty is encountered in usingv the rectifiers at elevated temperatures.

It is an object of my invention to provide. a copper-copper-oxide rectifier with which output potentials substantially greater than 6 volts shall be attainable.

Another object of my invention is to provide a copper-copper-oxide rectifier that shall operate without difficulty at elevated temperatures.

A further object of my invention is to decrease the space required by a copper-copper-oxide rectier arrangement for a given rating.

Still another object of my invention is tol provide a copper-copperoxide rectifier of simple structure.

More concisely stated, it is' an object of my invention to provide copper-copper-oxide rectiiiers that shall function satisfactorily within the range of potentials for which thermionic rectiers the difliculties encountered in using a prior art copper-copper-oxide rectifier may be primarily,

attributed to the fact that the element has a negative temperature coefficient.

current and a small reverse current. An increase in the temperature of the rectifier results in a decrease in both the forward resistance andthe back resistance so that when the temperature of a copper-copper-oxide rectifier increases, the forward current and the reverse current also increase. The increased current flow through the rectifier gives rise to a fur-ther increase in temperature and the result is that the resistance is further decreased and the current flow still further increased. This continues until the rectifier is damaged or completelydestroyed.

On analyzing the negative temperature coeicient, I have come to the conclusion that it arises from the presence of impurities in the copper from which the rectifier is formed. It appears that among the impurities lead is particularly objectionable. The impurities cannot be removed from the element without diiiiculty. Copper has a When a rectier is in operation it conducts substantial forward load relatively low vapor tension so that the impurities 55 are not easily ejected fromits surface. When the copper is heated at atmospheric pressure or in a relatively good vacuum in which the pressure is, for example, of the order of several millimeters, the impurities are oxidized and the undesirable proper-ties of the element are, as a matter of fact, increased.

In accordance with my invention the impurities are removed by heating the copper from which the rectifier is formed in a `high vacuum.' For the most satisfactory rectifiers, the pressure should be less than .1 micron. At times, however, satisfactory results have been attained with the copper heated in' a vacuum having as high a pressure as 30 microns. The heating should be carried out for severalhours at a temperature of the order of 1000 C. The temperature should preferably be between 900 C. and 1070 C., the fusing temperature of copper. YI have found, however, that heating at 700 C. produces sa-tisfactory -results, although the improvement increases with temperature and 'with the time interval during which the heating takes place. The novelfeatures that I consider characteristic of my invention are set forth with particularity in the appended claims. Theinvention tself, however, both as to its organization and its method of operation together with additional objects and advantages thereof. will best be under- A stood from the following discussion when read inv connection with the accompanyingdrawing, in which:

Figure l. shows the improvement attained with a rectifier produced in accordance with my invention; and

Fig. 2 shows an arrangement with which my invention may be practiced.

In'the practice of my invention, the principal feature is the heating of themetal in a high vacuum prior to i-ts oxidation. The copper base or blank is linitially in theform of a small disc or plate or in the form of a large plate from which a -number Vof .small discs or plates are stamped. Whatever the form, the surface is first cleansed of grease by the applicationl of carbontetra-chloride. The base is then dipped into concentrated nitric acid, and reused in distilled water. After the acid treatment, the .base is disposed in a vessel Which-is highly evacuated and heated for three hours at a temperature of from.

900 C; to 1000 C. `The pressure in the vessel is maintained at less than 1 micron and should preferably be .less than .1 micron.

. During the course of the treatment, the metal' gives up a number of impurities in its surface 2 andparticularly lead'. The impurities are emitted in a vaporous state, and will, of course, materially increase the pressure. For this reason, it is necessary that the vessel within which the plates are' flers formed in accordance with the practice of my invention show a vast improvement over prior art rectiers.

Rectifiers according to my invention are charproved rectiers designed for the same load are cordingly, after the three hour treatment, the

evacuated container is reduced to lroom tempera.-r ture and the blanks are removed and placed in .an oxidizing furnace. Here, the blanks are again heated and air orl oxygen-preferably at atmospheric pressure, is applied. 'Ihe oxidizing heat? ing is at a temperature of from 1020` C. to l030 C. and the treatment continues for 13 minutes. Of course, where convenient, the oxidizing treatment may be'carried out in the same furnace as the vacuum treatment. In such a case, it is unnecessary to reduce the blanks to room temperature.

After the 13 minute oxidizing treatment, the

A blanks are annealed at 500 C. for 13 minutes and then quenched in cold water. The surface of the copper is now coated with a layer which is predominantly cuprous oxide. Whatever cupric oxide happens to be present is now dissolved in the- I conventional manner and the usual contacts are applied.

A comparison of the characteristics of the vacuum treated copper-copper-oxide rectier and the present standard rectier is given in Figure 1.

The curves in this view are the result of actual tests carried out with a number of rectiers. In the upper right-hand quadrant, the current which flows through a short-circuited disc is plotted as a function of the potential for two limiting temperatures, '-40 C. and +40 C. Current isplotted vertically in amperes and potential is plotted horizontally in volts. The lower oblique full line curve 3 represents the function at 40 C. for the prior-art standard rectifier. The other oblique full line curve 5 represents. the function at 40 C. for the same rectier. It is to be noted that as the temperature of the rectifier changes the short-circuit current varies over a wide range. The large increase in the current flow for increase in temperature further increases'the temperature and tends to produce a. run-away effect.

The shaded area 1 between the oblique broken line curves 9 and Il represents the corresponding' range of variation for the rectifier according to `charge rectiiiers.

not necessary, and smallerunits may be used. The volume requirement of the necessary vacuum-treated rectiiiersv for a given load may be as muchas 1A@ of that required for the prior art rectiflersfused to supply the same load. Conversely, if the cooling fins are used with the improvedrectiers, and the same number of improved rectiflers as prior art rectiflers are used, the increase in the output rating for the improved rectiers is 6 to 8 times the output rating of the prior art rectiiiers.

My invention also. 'makes possible the use of dry vrectifier units at-moderately high potentials where appreciable power is required. A rectifier, in accordance with my invention, has been used to supply .7 ampere direct current at 1500 volts continuously. The dimensions of this rectifier are 15" x 155 lx 3" and when operated at the aforementioned rating, its eiilciency was greater than 80%.

Because of the improvement which is introduced by my invention and the saving in cost which is effected, the improved 'rectiers may be sold in competition with gaseous or vacuum dis- Over such rectifiers, the copper-copper-oxide rectiers have a number of marked advantages. For example, the danger of sudden failure by reason of failure of the filament, is absent. No heating time for a filament is necessary. The copper-copper-oxide rectifier is, moreover, a solid object and can withstand shock such as is experienced on board of a battle ship, for example, by reason of gun-fire,better than the glass tube rectiers.

The system with which the vacuum treatment is carried out in accordance with my invention is lshown in Figure 2. The copper blanks are, in

this case, in the form of plates, 25. The blanks are mounted in a rack 21 which is disposed in a cylindrical container 29, preferably composed of a. nickel-chromiumA alloy, sold under the trade name Nichrome."V The cylinder is provided with my invention. In this case, it is to be noted that the range of variation is materially smaller.

In the lower left-hand. quadrant the back current is plotted as a function of the back potential. In this case, current is plotted vertically in milliamperes and potential horizontally in volts. The

full line curve I5 which is at a very small angle ing the shaded area 23 represent the situationl for the rectifier according to my invention 40 C. and 40 C. respectively. It is seen that rectian opening 3i at one end, through which the rack 21 is inserted and which is closed by a metal plate 33. The neck 25 of the cylinder 29 and the plate 33 are supplied with cooling water 31 which prevents these portions from becoming over-heated.

The cylinder 29 is in communication with a suitable vacuum pump 39 through an outlet 4I in the neck 35. The pump 39 may operate alone or a mechanical pump may be interposed in series with it.

The temperature of the container 29 and its content is raised electrically by a resistance' heater 43 embedded in an insulator 45 which is disposed around the container. To determine the temperature within` the container, a thermocouple l1 is provided.

While in the preferred practice of my inven-- tion the copper blanks are vacuum treated, there are alternative procedures. Foi example, the copper melt, before being cast into an ingot, may. be vacuum treated to produce the desired characteristics. 0f course. thevacuum treatment should be the same as inthe case of the solid blank. That is, to say, the pressure should be maintained preferably at less'than .1 micron.

Although I have illustrated and described certain methods of treatment in accordance with my invention, I am fully aware that many modiiications thereof are possible. My invention. therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

l. The method of preparinga blank copper discfor oxidation, 'to produce a copper-copperoxide disc, which includes the step of heating said blank disc in a vacuum for several hours at a pressure of less than 30 microns and at a temperature of from ture of copper.

2. The method of preparing a blank copper 700 C. to the fusing tempera.

disc for oxidation, to produce a copper-copperoxide disc, which includes the step of'heating saidblank disc in a vacuumfor a time interval ofthe order of two hours at a pressure of less than 30 microns and at a temperature of from 700 C. to the fusing temperature of copper.

3. The method of preparing a blank copper disc for oxidation, to produce a copper-copperoxide disc, which includes the step of heating said blank disc in a vacuum for a time interval of the order of two hours at a pressure of less than .1 micron at atemperaturel of from '700 C. to the fusing temperature of copper.

4. The method of preparingv a copper-copperoxide rectifier disc from a copper disc, which comprises the steps of cleansing said copper disc to remove grease and the like from the surface, heating the cleansed copper disc for a time interval of the order of three hours at a temperaan oxidizing atmosphere at a temperature of 1020 C. to 1030 C. for a time interval of the' order of 13 minutes, annealing the discthus oxidized by heating at 500 C. fora/time interval of the order vof 11i-minutes and quenching the annealed disc, in acold uid.

5. In'the production of a copper-copper-oxide rectier disc, the method of preparing a blank copper disc for oxidation which includes the step o f heating said blank copper disc in a vacuum for a time interval greater than one hour at a. pressure of less than 30 microns and at a temperature of from 700, C. to the fusing temperature of copper.

6. In the production of a copper-copper-oxide rectifier disc, the method of preparing a blank copper disc for oxidation which includes the step of maintaining the melt from which the blank copper discs are to be formed at a pressure of less than 30Y microns for a substantial time interval.

ture of from 700 C. to the fusing temperature Y of copper in a vacuum at pressure of less than 30 microns thereafter heating. the copper disc in 7. The process of producing copperoxide rectier elements which comprises the stepseof vacuum-treatingfmoltn icopper; Vcongealing said copper; and subsequently oxidizing its surface.

8. The process of producing copper-oxide rectifier elements which comprises the steps of vacuum-treating molten copper in an enclosure: which has been exhausted toa pressure .not exceeding the-order of 30 microns, congealing said copper, and subsequently oxidizing its' surface.

9.V In the production of a copper-copper-oxide rectier disc, the method of preparing. a blank copper disc for oxidation which includes the step of heating said blank copper 'disc in a vacuum for a time interval at least'of the order of one hour at a pressure of less than 30-microns and at a temperature of from 700 C. to the fusingv temperature of copper.

' CARL C. HEIN.v 

